Insulated top cover of a large-scale water pit for heat storage: A structure, materials, and performance review

Among the many clean heating technologies with solar energy as the main energy source, a water pit for solar seasonal heat storage and heating technology has been actively promoted by many countries due to its reliable technology and mature engineering applications. The insulated top cover is the most important, critical, and expensive component of the water pit for solar heat storage. In this paper, the structural design, material application, and evaluation methods of an insulated top cover were reviewed based on scientific references and practical projects. First, the whole type and split type structure forms of the insulated top cover were summarized, and the applicable scenes of different structural forms were pointed out. Second, the performance analysis of impermeable materials and insulation materials of the insulated top cover was carried out, and the performance characteristics of the corresponding materials as well as the problems to be solved were pointed out. Finally, the performance evaluation method of the insulated top cover was comprehensively analyzed, and it was pointed out that there is still a lack of scientific and efficient evaluation parameters and monitoring methods for an insulated top cover in line with engineering practice. The purpose of this paper was to provide reference for the scientific research and engineering application of a water pit for solar seasonal heat storage and heating technology.